The invention relates generally to the field of medical ventilators or, more specifically, to the control of such ventilators.
A medical ventilator delivers gas to a patient""s respiratory tract and is often required when the patient is unable to maintain adequate ventilation. Mechanical ventilation is the single most important therapeutic modality in the care of critically ill patients. Known ventilators typically include a pneumatic system that delivers and extracts gas pressure, flow and volume characteristics to the patient and a control system (typically consisting of knobs, dials and switches) that provides the interface to the treating clinician. Optimal support of the patient""s breathing requires adjustment by the clinician of the pressure, flow, and volume of the delivered gas as the condition of the patient changes. Such adjustments, although highly desirable, are difficult to implement with known ventilators because the control system demands continuous attention and interaction from the clinician.
Further, patients requiring ventilatory assistance must overcome airway resistance in the breathing circuit during exhalation. This resistance, combined with the stiffness of the lungs and the thoracic cage under certain pathological conditions, imposes a significant workload upon a patient whose reserves may already be compromised by underlying disease processes.
The invention relates to a medical mechanical ventilator device adapted for use in weaning a patient from mechanical ventilation. In one embodiment, the device measures the patient""s minute volume, breath frequency, and detects a patient""s spontaneous breath. The device compares the patient""s minute volume and the patient breath rate to a predetermined minute volume and a predetermined breath rate entered by a clinician. In a pressure support mode, the device decreases patient pressure support level if the patient""s spontaneous breathing rate falls within the predetermined range of breathing and the patient""s minute volume exceeds the predetermined minute volume. In one embodiment, the patient""s spontaneous breathing rate and the patient""s minute volume is determined on a breath-by-breath basis. For the purposes of this invention, intrabreath is defined as within the period of one breath cycle, and interbreath is defined as within the period of at least two breaths.
In another embodiment, the invention is a ventilator system adapted for use in weaning a patient from mechanical ventilation. The ventilator system comprises a pressure source in communication with the patient""s respiratory system to provide pressure support to the patient. The device further comprises a breath frequency monitor, a minute volume flow meter, an input device, and a data processing unit. The data processing unit compares the patient""s breathing frequency and patient""s minute volume to the breathing frequency and minute volume entered by the clinician. Pressure support is adjusted by the ventilator on an intrabreath or interbreath basis.